Optical integrator, illumination optical device, exposure apparatus, and exposure method

ABSTRACT

An optical integrator having characteristics to reduce effects of manufacturing errors of many minute refraction surfaces integrally formed by, for example, etching on an illumination intensity distribution. An optical integrator ( 8 ) comprising an integrally formed plurality of first minute refraction surfaces ( 80   a ) and an integrally formed plurality of second minute refraction surfaces ( 80   b ). A parameter β satisfies conditions, |β|&lt;0.2 (where β=(γ−1) 3 ·NA 2 /Δn 2 ), where a refracting power ratio φa/φb between φa, a refracting power of the first minute refraction surfaces and φb, a refracting power of the second minute refraction surfaces is γ, numerical aperture on an emission side of the optical integrator is NA, and a difference between a refraction index of a medium on a light entrance side of the second minute refraction surfaces and a refraction index of a medium on a light emission side of the second minute refraction surfaces is Δn.

TECHNICAL FIELD

The present invention relates to an optical integrator, an illuminationoptical device, an exposure apparatus, and an exposure method, and moreparticularly to an illumination optical device suitable for an exposureapparatus for manufacturing micro devices such as a semiconductordevice, an image pickup device, a liquid crystal display device, and athin film magnetic head in a lithography step.

BACKGROUND ART

In a typical exposure apparatus of this kind, a light beam emitted froma light source enters a fly's eye lens. Then, a secondary light sourceconstructed from many light sources is formed on the rear side focalsurface thereof. A light beam from the secondary light source is limitedthrough an aperture stop arranged in the vicinity of the rear side focalsurface of the fly's eye lens, and then, enters a condenser lens. Theaperture stop limits a shape or a size of the secondary light source toa desired shape or a desired size according to desired illuminationconditions (exposure conditions).

A light beam condensed by the condenser lens illuminates in a state ofsuperimposition a mask in which a given pattern is formed. Light passingthrough the pattern of the mask forms an image on a wafer through aprojection optical system. Thereby, the mask pattern is projected andexposed (transferred) on the wafer. The pattern formed on the mask ishighly integrated. Therefore, in order to correctly transfer this finepattern on the wafer, it is essential to obtain a uniform illuminationintensity distribution on the wafer.

In the exposure apparatus having the foregoing construction, it isnecessary to set minute lens elements constructing the fly's eye lens asmuch as possible in order to improve uniformity of the illuminationintensity distribution. Further, it is necessary to form the secondarylight source in the shape close to a desired shape in order to avoidlight amount loss in the aperture stop. Therefore, for example, it isthinkable that a size of the minute lens element constructing the fly'seye lens is set very small, that is, a micro fly's eye lens is used.

The fly's eye lens is constructed by arranging many lens elementsvertically and horizontally and densely. Meanwhile, the micro fly's eyelens is constructed by integrally forming many minute refractionsurfaces. That is, the fly's eye lens is constructed by combining anddensely arranging many single polished lens elements. Meanwhile, themicro fly's eye lens is constructed by forming many minute refractionsurfaces on, for example, a parallel plane glass plate by applying MEMStechnique (lithography plus etching and the like).

Therefore, the fly's eye lens can be manufactured by checking refractionsurface shapes of polished lens elements, selecting lens elementsmeeting standards, and using only lens elements having a high-preciselyformed refraction surface. However, in the micro fly's eye lens, allminute refraction surfaces are required to be concurrently manufacturedby etching through which is hard to obtain a quality surface shapecompared to polishing. Therefore, a straight pass ratio thereof becomesconsiderably lower than that of the fly's eye lens.

In view of the foregoing problem, it is an object of the invention toprovide an optical integrator having characteristics to reduce theeffects of manufacturing errors of many minute refraction surfacesintegrally formed by etching or the like on an illumination intensitydistribution. Further, it is another object of the invention to providea highly efficient illumination optical device capable of illuminatingan irradiated surface under desired illumination conditions by using theoptical integrator, wherein the effects of the manufacturing errors ofthe minute refraction surfaces on the illumination intensitydistribution are reduced. Further, it is still another object of theinvention to provide an exposure apparatus and an exposure methodcapable of performing good projection exposure under good illuminationconditions by using the highly efficient illumination optical devicecapable of illuminating the irradiated surface under the desiredillumination conditions.

DISCLOSURE OF THE INVENTION

In order to solve the foregoing problem, a first invention of thepresent invention provides an optical integrator, comprising:

an integrally formed plurality of first minute refraction surfaces; and

an integrally formed plurality of second minute refraction surfaces,which are provided closer to a light emission side than the plurality offirst minute refraction surfaces so that the plurality of second minuterefraction surfaces optically correspond to the plurality of firstminute refraction surfaces, wherein a parameter β satisfies thefollowing conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where

a refracting power ratio φa/φb between φa, a refracting power of thefirst minute refraction surfaces and φb, a refracting power of thesecond minute refraction surfaces is γ, numerical aperture on theemission side of the optical integrator is NA, and a difference betweena refraction index of a medium on a light entrance side of the secondminute refraction surfaces and a refraction index of the medium on alight emission side of the second minute refraction surfaces is Δn.

According to a preferable aspect of the first invention, the pluralityof first minute refraction surfaces and the plurality of second minuterefraction surfaces are formed on the same optical member. Otherwise,the optical integrator comprises: a first optical member having theplurality of first minute refraction surfaces; and a second opticalmember having the plurality of second minute refraction surfacesarranged on a light emission side of the first optical member. Further,according to the preferable aspect of the first invention, the pluralityof second minute refraction surfaces comprise aspherical surfaces.

A second invention of the present invention provides an opticalintegrator, comprising in the order from a light entrance side:

a first optical member having an integrally formed plurality of firstminute refraction surfaces; and

a second optical member having an integrally formed plurality of secondminute refraction surfaces, which are provided to optically correspondto the plurality of first minute refraction surfaces, wherein

a refraction index of an optical material forming the second opticalmember is set larger than a refraction index of an optical materialforming the first optical member.

According to a preferable aspect of the second invention, the opticalintegrator satisfies a condition, 0.05≦nb−na, where the refraction indexof the optical material forming the first optical member is na, and therefraction index of the optical material forming the second opticalmember is nb. Further, it is preferable that the optical integrator isused for light having a wavelength of 300 nm or less, and the opticalmaterial forming the first optical member includes silica glass orfluorite, and the optical material forming the second optical memberincludes one material of magnesium oxide, ruby, sapphire, quartzcrystal, and silica glass. Otherwise, it is preferable that the opticalintegrator is used for light having a wavelength of 300 nm or less, andthe optical material forming the first optical member includes fluorite,and the optical material forming the second optical member includessilica glass. Further, in the first invention and the second invention,it is preferable that each minute refraction surface is formedspherically or aspherically. Further, it is preferable that thisaspherical surface is a rotational symmetry aspherical surface or arotational asymmetry aspherical surface (for example, a cylindricalsurface).

A third invention of the present invention provides an illuminationoptical device for illuminating an irradiated surface, comprising: theoptical integrator of the first invention or the second invention. Inthis case, it is preferable that the optical integrator forms a lightintensity distribution in a given shape in an illumination region.

A fourth invention of the present invention provides an exposureapparatus, comprising: the illumination optical device of the thirdinvention; and a projection optical system for projecting and exposing apattern of a mask arranged on the irradiated surface on a photosensitivesubstrate.

According to a preferable aspect of the fourth invention, the pattern ofthe mask is projected and exposed on the photosensitive substrate byrelatively moving the mask and the photosensitive substrate in relationto the projection optical system along a scanning direction, and anabsolute value of the parameter β in terms of a direction opticallyapproximately perpendicular to the scanning direction is set lower thanan absolute value of the parameter β in terms of the scanning direction.

A fifth invention of the present invention provides an exposure method,wherein a mask is illuminated through the illumination optical device ofthe third invention, and wherein an image of a pattern formed on theilluminated mask is projected and exposed on a photosensitive substrate.

A sixth invention of the present invention provides an exposureapparatus, comprising:

an illumination optical system including an optical integrator; and

a projection optical system for forming a pattern image of a mask on aphotosensitive substrate, wherein

the pattern of the mask is projected and exposed on the photosensitivesubstrate while the mask and the photosensitive substrate are relativelymoved in relation to the projection optical system along a scanningdirection, wherein

the optical integrator comprises: an integrally formed plurality offirst minute refraction surfaces; and an integrally formed plurality ofsecond minute refraction surfaces, which are provided closer to a lightemission side than the plurality of first minute refraction surfaces sothat the plurality of second minute refraction surfaces opticallycorrespond to the plurality of first minute refraction surfaces, andwherein

a parameter β satisfies the following conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where

a refracting power ratio φa/φb between φa, a refracting power of thefirst minute refraction surfaces in terms of a nonscanning directionoptically approximately perpendicular to the scanning direction and φb,a refracting power of the second minute refraction surfaces in terms ofthe nonscanning direction is γ, numerical aperture on the emission sidein terms of the nonscanning direction of the optical integrator is NA,and a difference between a refraction index of a medium on a lightentrance side of the second minute refraction surfaces and a refractionindex of the medium on a light emission side of the second minuterefraction surfaces is Δn.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view explaining a basal principle of the invention;

FIG. 2 is a view explaining optical characteristics in a micro fly's eyelens of FIG. 1;

FIG. 3 is a view schematically showing a construction of an exposureapparatus comprising an illumination optical device according to anembodiment of the invention;

FIG. 4 is a view schematically showing a construction of a micro fly'seye lens of FIG. 3;

FIG. 5 is a perspective view schematically showing a construction of acylindrical micro fly's eye lens according to a first modification ofthe embodiment;

FIG. 6 is a view schematically showing a construction of a micro fly'seye lens according to a second modification of the embodiment;

FIG. 7 is a flowchart of a technique in obtaining a semiconductor deviceas a micro device; and

FIG. 8 is a flowchart of a technique in obtaining a liquid crystaldisplay device as a micro device.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a view explaining a basal principle of the invention.Referring to FIG. 1, light supplied from a light source S providesKoehler illumination for a micro fly's eye lens MF through a firstcondenser optical system C1. The micro fly's eye lens MF comprises afirst subsystem A and a second subsystem B in the order from the lightsource S side. Many first minute refraction surfaces are integrallyformed in the first subsystem A, and many second minute refractionsurfaces are integrally formed in the second subsystem B so that thesecond minute refraction surfaces optically correspond to the firstminute refraction surfaces.

Therefore, light whose wavefront is segmented by the respective minuterefraction surfaces of the micro fly's eye lens MF reaches anillumination field I on an irradiated surface through a second condenseroptical system C2. Here, an optical conjugate relation is establishedbetween an entrance surface A1 of the micro fly's eye lens MF (that is,an entrance surface of the first subsystem A) and the illumination fieldI. Therefore, a light intensity distribution in a region correspondingto each minute refraction surface on the entrance surface A1 isrespectively expanded and projected on the whole illumination field I.FIG. 1 shows a model of only light ray corresponding to one minuterefraction surface. However, in practice, the whole illumination field Iis illuminated in a state of superimposition through many minuterefraction surfaces, and thereby uniformity of illumination intensitycan be obtained over the whole illumination field I.

In the illumination system shown in FIG. 1, there is the conjugaterelation between the entrance surface A1 of the micro fly's eye lens MFand the illumination field I. However, when a distortion aberration ofan imaging system P (micro fly's eye lens MF plus second condenseroptical system C2) is changed, an imaging magnification varies accordingto an image height. Therefore, the illumination intensity distributionin the illumination field I becomes changed. For example, according toIsshiki Masaki, “Image Surface Illumination Intensity Distribution ofPhotographic Lens”, Optical Technology Contact Vol. 5, No. 11, pp.10-14, 1967, it is known that when the distortion aberration of theimaging system P is changed by D %, the illumination intensity in theillumination field (image surface of the imaging system P) I is changedby about 4D %.

As an evaluation method for the aberration of the imaging system(including the distortion aberration), aberration evaluation method bythird order aberration theory is known. Analysis of the aberration bythe third order aberration theory has an advantage that evaluation isfacilitated since analytical calculation is enabled in spite of errorsdue to approximation. Details of derivation method of an aberrationcoefficient by the third order aberration theory are, for example,described in Matsui Yoshiya, “Aberration Theory,” Japan OptoelectroMechanics Association, 1989. Discussion will be hereinafter given ofchange of the distortion aberration of the imaging system P lyingbetween the entrance surface A1 of the micro fly's eye lens MF and theillumination field I when surface shapes of the minute refractionsurfaces of the micro fly's eye lens MF are changed by using the thirdorder aberration theory.

A surface shape of each minute refraction surface in the micro fly's eyelens MF is expressed by the following Formula (1), where a height in thedirection perpendicular to an optical axis is y, a distance (sag amount)along the optical axis between a tangent plane on the top of therefraction surface and a position on the refraction surface in theheight y is x, a curvature is c, and a conic coefficient is κ.x=(c·y ²)/[1+{1−(κ+1)c ² ·y ²}^(1/2)]  (1)

According to the third order aberration theory, any aberrationcoefficient can be expressed by a sum of a spheric term and an asphericterm. Variations of surface shapes in manufacturing the micro fly's eyelens MF appear as change of the curvature c and the conic coefficient κin the foregoing formula (1). Here, the change of the curvature caffects a size of illumination, but does not affect illuminationnonuniformity practically. Meanwhile, the change of the coniccoefficient κ changes the aspheric term of the aberration coefficient,and affects the illumination nonuniformity.

According to the foregoing Matsui Yoshiya, “Aberration Theory”, V_(asp),an aspheric term of the distortion aberration coefficient of objectimaging is generally expressed by the following Formula (2). In Formula(2), h_(i) represents a light ray height of an image paraxial tracingvalue (light ray height in tracing an object (image) paraxial ray(paraxial ray related to the object (the image))), and h_(p) representsa light ray height of a pupil paraxial tracing value (light ray heightin tracing a pupil paraxial ray (paraxial ray related to the pupil)). Ψrepresents a coefficient expressed by the next Formula (3).V _(asp) =h _(i) ·h _(p) ³·Ψ  (2)Ψ=Δn·c ³·κ  (3)

Here, Δn represents a difference between a refraction index of a mediumon the light entrance side of the minute refraction surfaces and arefraction index of a medium on the light emission side of the minuterefraction surfaces. Δn represents a value obtained by subtracting n1, arefraction index of the medium on the light entrance side of the minuterefraction surfaces from n2, a refraction index of the medium on thelight emission side of the minute refraction surfaces (n2−n1). FIG. 2 isa view explaining optical characteristics in the micro fly's eye lens ofFIG. 1. In FIG. 2, a refracting power (power) of the micro fly's eyelens MF is expressed by φ, a refracting power of the first subsystem Ais expressed by φa, a refracting power of the second subsystem B isexpressed by φb, and an air conversion surface-to-surface distancebetween the first subsystem A and the second subsystem B is expressed bys.

Therefore, relations shown in the following Formulas (4a) to (4d) areestablished, where φ, the refracting power of the micro fly's eye lensMF is standardized to 1, and a refracting power ratio φa/φb between φa,the refracting power of the first subsystem A and φb, the refractingpower of the second subsystem B is γ.φ=1  (4a)φa=γ  (4b)φb=1  (4c)s=1  (4d)

Paraxial tracing values then are shown in the following Table 1.

TABLE 1 Height of Height of ray Image ray Pupil related conversionrelated conversion to the obliquity to the obliquity image h_(i) α_(i)pupil h_(p) α_(p) First 0 −1 −1 0 subsystem A Second 1 −1 γ − 1 −γsubsystem B

Referring to Table 1 and Formulas (2) and (3), V_(aspA), an asphericterm of the distortion aberration coefficient in the first subsystem Aand V_(aspB), an aspheric term of the distortion aberration coefficientin the second subsystem B are expressed by the following Formulas (5)and (6) respectively.V_(aspA)=0  (5)V _(aspB)=(γ−1)³ ·Δn·c ³ ·κ  (6)

Referring to Formulas (5) and (6), it is found that change of theaspheric term of the distortion aberration coefficient caused byvariations of surface shapes of the minute refraction surfaces of themicro fly's eye lens MF (that is, change of the conic coefficient κ) isgenerated only in the second subsystem B in the range of the third orderaberration. Next, discussions will be given of effects of the change ofthe aspheric term of the distortion aberration coefficient on theillumination intensity distribution in the illumination field I. In thesecond subsystem B, the proportionality relation shown in the followingFormula (7) is established between the curvature c and the refractionindex difference Δn.c∝1/Δn  (7)

In the range of the third order aberration, the illumination intensitydistribution in the illumination field I is changed in proportion to asquare value of the image height. The image height is proportional tonumerical aperture NA on the emission side of the micro fly's eye lensMF. Therefore, based on Formulas (5) to (7), change of the distortionaberration caused by change of surface shapes of the minute refractionsurfaces of the micro fly's eye lens MF, then β, sensitivity of changeof the illumination intensity distribution on the illumination field(image surface) I is expressed by the following Formula (8).β=(γ−1)³ ·NA ² /Δn ²  (8)

When the micro fly's eye lens MF is arranged in the air, Formula (8) canbe transformed into the following Formula (8′), where a refraction indexof an optical material forming the second subsystem B is n.β=(γ−1)³ ·NA ²/(n−1)²  (8′)

Thereby, it is possible to reduce change of the distortion aberrationcaused by variations of surface shapes of the minute refraction surfacesof the micro fly's eye lens MF, and to reduce effects on theillumination intensity distribution in the illumination field I byreducing an absolute value of the parameter β. In other words, it ispossible to realize a micro fly's eye lens (optical integrator) MFhaving characteristics, wherein effects of manufacturing errors of manyminute refraction surfaces integrally formed by etching or the like onthe illumination intensity distribution are reduced by reducing theabsolute value of the parameter β.

Referring to Formula (8), it is thinkable that the absolute value of theparameter β can be reduced by increasing the refracting power ratio γ,increasing the refraction index difference Δn, and reducing thenumerical aperture NA on the emission side of the micro fly's eye lensMF. However, when the refracting power ratio γ is increased and getsclose to 1, the risk that an energy density on an entrance surface B2 ofthe micro fly's eye lens MF (that is, emission surface of the secondsubsystem B) is increased and then the second subsystem B is damaged bylight energy irradiation becomes increased.

Further, the numerical aperture NA on the emission side of the microfly's eye lens MF is determined by a size of an illumination region anda focal length of the second condenser optical system C2. In general,there is no design flexibility to set the numerical aperture NA on theemission side of the micro fly's eye lens MF to a desired small valuewithout changing the size of the illumination region and the focallength of the second condenser optical system C2. In result, in theinvention, such a technique is adapted that the refraction indexdifference Δn in the second subsystem B is set large. However, the costis easily increased along with increase of the refraction index of theoptical material. Therefore, it is realistic that an optical materialhaving a high refraction index is used only for the second subsystem B.

Therefore, in the invention, nb, a refraction index of an opticalmaterial forming the second subsystem B (second optical member) is setlarger than na, a refraction index of an optical material forming thefirst subsystem A (first optical member). In this case, in order to welldemonstrate effects of the invention, it is preferable that therefraction index na and the refraction index nb satisfy a condition of0.05≦nb−na. More specifically, when the first subsystem A is formed bysilica glass or fluorite, it is preferable that the second subsystem Bis formed by magnesium oxide, ruby, sapphire, quartz crystal, or silicaglass. When the first subsystem A is formed by fluorite, it ispreferable that the second subsystem B is formed by silica glass.

According to a simulation based on a design numerical value example, inthe case of a typical micro fly's eye lens MF, wherein a size(dimension) of each minute refraction surface is 0.7 mm and numericalaperture NA on the emission side is 0.25, it was found that it wasdifficult to obtain a surface shape error of the minute refractionsurfaces of 50 nm or less, and in this case, when the absolute value ofthe parameter β was larger than 0.2, variations of illuminationintensity in the illumination field (image surface) I tended to becomelarge as much as intolerable.

Therefore, in the invention, change of the distortion aberration causedby variations of surface shapes of the minute refraction surfaces of themicro fly's eye lens MF is reduced, and then effects on the illuminationintensity distribution in the illumination field I are reduced bysetting the absolute value of the parameter β lower than 0.2. In orderto further reduce effects of the manufacturing error of the minuterefraction surfaces on the illumination intensity distribution, it ispreferable that the upper limit value of the absolute value of theparameter β is set to 0.13. In some cases, it is necessary to highlycontrol the illumination intensity distribution in the illuminationregion in the illumination system. In this case, it is preferable thatthe absolute value of the parameter β is set lower than 0.2, and theminute refraction surfaces of the second subsystem B are aspheric.Thereby, it becomes possible to control the distortion aberration of theimaging system P (micro fly's eye lens MF plus second condenser opticalsystem C2). Then, it becomes possible to approximate the illuminationintensity distribution in the illumination region to a desireddistribution.

An embodiment of the invention will be described with reference to theattached drawings.

FIG. 3 is a view schematically showing a construction of an exposureapparatus comprising an illumination optical device according to theembodiment of the invention. In FIG. 3, Z axis is set along the normalline of a wafer W, a photosensitive substrate, Y axis is set in thedirection parallel to a paper space of FIG. 3 in a wafer face, and Xaxis is set in the direction perpendicular to the paper space of FIG. 3in the wafer face respectively. In FIG. 3, the illumination opticaldevice is set to perform annular illumination.

The exposure apparatus of FIG. 3 comprises, for example, a KrF excimerlaser light source for supplying light having a wavelength of 248 nm, oran ArF excimer laser light source for supplying light having awavelength of 193 nm as a light source 1. An almost parallel light beamemitted from the light source 1 along the Z direction has a rectangularcross section longly extending along the X direction. The light beamenters a beam expander 2 constructed from a pair of lenses 2 a and 2 b.The respective lenses 2 a and 2 b have a negative refracting power and apositive refracting power in the paper space (YZ plain) of FIG. 3respectively. Therefore, the light beam entering the beam expander 2 isexpanded in the paper space of FIG. 3, and shaped into a light beamhaving a given rectangular cross section.

An almost parallel light beam through the beam expander 2 as a opticalshaping system is deflected in the Y direction by a deflecting mirror 3,and then enters an afocal zoom lens 5 through a diffractive opticalelement 4. In general, the diffractive optical element is constructed byforming steps having a pitch of about a wavelength of exposure light(illumination light) on a glass substrate. The diffractive opticalelement has an action for diffracting an incident beam at a desiredangle. More specifically, when a parallel light beam having arectangular cross section enters the diffractive optical element 4, thediffractive optical element 4 has a function to form a circular lightintensity distribution in a far field thereof (or Fraunhofer diffractionregion). Therefore, the light beam through the diffractive opticalelement 4 forms the circular light intensity distribution, that is, alight beam having a circular cross section in the position of a pupil ofthe afocal zoom lens 5.

The diffractive optical element 4 is constructed to be able to retreatfrom an illumination optical path. The afocal zoom lens 5 is constructedto be able to continuously change magnifications in a given range whilemaintaining an afocal system (afocal optical system). A light beamthrough the afocal zoom lens 5 enters a diffractive optical element 6for annular illumination. The afocal zoom lens 5 optically and almostconjugately connects a divergence original point of the diffractiveoptical element 4 and a diffractive surface of the diffractive opticalelement 6. Numerical aperture of the light beam focusing on one point ofthe diffractive surface of the diffractive optical element 6 or thesurface in the vicinity thereof varies according to magnifications ofthe afocal zoom lens 5.

When a parallel light beam enters the diffractive optical element 6 forannular illumination, the diffractive optical element 6 for annularillumination has a function to form a ring light intensity distributionin a far field thereof. The diffractive optical element 6 is constructedremovably from the illumination optical path. In addition, thediffractive optical element 6 is constructed changeably with adiffractive optical element 60 for quadrupole illumination or adiffractive optical element 61 for circular illumination. A light beamthrough the diffractive optical element 6 enters a zoom lens 7. In thevicinity of a rear side focal surface of the zoom lens 7, an entrancesurface of a micro fly's eye lens 8 constructed from a first fly's eyemember 8 a and a second fly's eye member 8 b in the order from the lightsource side (that is, entrance surface of the first fly's eye member 8a) is positioned. The micro fly's eye lens 8 functions as an opticalintegrator forming many light sources based on the incident light beam.Its detailed construction and action will be described later.

As described above, the light beam from the circular light intensitydistribution formed in the position of the pupil of the afocal zoom lens5 through the diffractive optical element 4 is emitted from the afocalzoom lens 5. After that, the emitted light beam becomes a light beamhaving various angle elements, which enters the diffractive opticalelement 6. Therefore, the light beam through the diffractive opticalelement 6 forms, for example, an annular illumination field centering onan optical axis AX on the rear side focal surface of the zoom lens 7(then on the entrance surface of the micro fly's eye lens 8).

An outer diameter of the annular illumination field formed on theentrance surface of the micro fly's eye lens 8 varies according to focallengths of the zoom lens 7. Therefore, the zoom lens 7 practicallyconnects the diffractive optical element 6 and the entrance surface ofthe micro fly's eye lens 8 in a state of Fourier transformationrelation. A light beam entering the micro fly's eye lens 8 issegmentalized two-dimensionally. Many light sources (hereinafterreferred to as “secondary light source”) in the same annular state as inthe illumination field formed by the incident light beam are formed onthe rear side focal surface thereof.

A light beam from the annular secondary light source formed on the rearside focal surface of the micro fly's eye lens 8 receives a condensingaction of a condenser optical system 9, and then illuminates in a stateof superimposition a mask M, wherein a given pattern is formed. A lightbeam passing through the pattern of the mask M forms an image of themask pattern on the wafer W, the photosensitive substrate through aprojection optical system PL. Thereby, the pattern of the mask M issequentially exposed in each exposure region of the wafer W byperforming exposure in batch or scanning exposure whiletwo-dimensionally drive-controlling the wafer W in the plane (XY plane)perpendicular to the optical axis AX of the projection optical systemPL.

In the exposure in batch, the mask pattern is exposed in batch for eachexposure region of the wafer according to so-called step and repeatmethod. In this case, a shape of the illumination region on the mask Mis a rectangle close to a square. Meanwhile, in the scanning exposure,the mask pattern is scanned and exposed for each exposure region of thewafer while the mask and the wafer are relatively moved in relation tothe projection optical system according to so-called step and scanningmethod. In this case, a shape of the illumination region on the mask Mis a rectangle, wherein a ratio between a short side and a long side is,for example, 1:3.

In this embodiment, when a magnification of the afocal zoom lens 5 ischanged, a center height of the annular secondary light source (distancebetween a center line of the circle and the optical axis AX) is notchanged, but only a width thereof (½ of a difference between an outerdiameter (diameter) and an internal diameter (diameter)) is changed.That is, it is possible to change both a size (outer diameter) and ashape (annular ratio: internal diameter/outer diameter) of the annularsecondary light source by changing magnifications of the afocal zoomlens 5.

Further, when the focal length of the zoom lens 7 is changed, theannular ratio of the annular secondary light source is not changed, butboth the center height and the width thereof are changed. That is, it ispossible to change an outer diameter of the annular secondary lightsource without changing the annular ratio thereof by changing the focallength of the zoom lens 7. Therefore, in this embodiment, only theannular ratio of the annular secondary light source can be changedwithout changing the outer diameter thereof by changing magnificationsof the afocal zoom lens 5 and focal lengths of the zoom lens 7 asappropriate.

As described above, the diffractive optical element 6 is constructedremovably from the illumination optical path. In addition, thediffractive optical element 6 is constructed changeably with thediffractive optical element 60 for quadrupole illumination or thediffractive optical element 61 for circular illumination. Descriptionwill be hereinafter given of the quadrupole illumination obtained bysetting the diffractive optical element 60 in the illumination opticalpath instead of the diffractive optical element 6. When a parallel lightbeam enters the diffractive optical element 60 for quadrupoleillumination, the diffractive optical element 60 for quadrupoleillumination has a function to form a four point light intensitydistribution in a far field thereof. Therefore, a light beam through thediffractive optical element 60 forms a quadrupole illumination fieldconstructed from four circular illumination fields centering on, forexample, the optical axis AX on the entrance surface of the micro fly'seye lens 8. In result, the same quadrupole secondary light source as inthe illumination field formed on the entrance surface of the micro fly'seye lens 8 is formed on the rear side focal surface of the micro fly'seye lens 8.

As in the case of the annular illumination, it is also possible in thequadrupole illumination that both an outer diameter of the quadrupolesecondary light source (diameter of a circumscribed circle of fourcircular surface light sources) and an annular ratio thereof (diameterof an inscribed circle of the four circular surface lightsources/diameter of the circumscribed circle of the four circularsurface light sources) are changed by changing magnifications of theafocal zoom lens 5. Further, it is possible to change the outer diameterof the quadrupole secondary light source without changing the annularratio thereof by changing the focal length of the zoom lens 7. Inresult, only the annular ratio of the quadrupole secondary light sourcecan be changed without changing the outer diameter of the quadrupolesecondary light source by changing magnifications of the afocal zoomlens 5 and focal lengths of the zoom lens 7 as appropriate.

Next, descriptions will be given of the circular illumination obtainedby retiring the diffractive optical element 4 from the illuminationoptical path and setting the diffractive optical element 61 for circularillumination in the illumination optical path instead of the diffractiveoptical elements 6 or 60. In this case, a light beam having arectangular cross section enters the afocal zoom lens 5 along theoptical axis AX. The light beam entering the afocal zoom lens 5 isexpanded or reduced according to the magnification, is emitted from theafocal zoom lens 5 along the optical axis AX while being the light beamhaving the rectangular cross section as it is, and enters thediffractive optical element 61.

Here, similarly to the diffractive optical element 4, when a parallellight beam having a rectangular cross section enters the diffractiveoptical element 61 for circular illumination, the diffractive opticalelement 61 for circular illumination has a function to form a circularlight intensity distribution in a far field thereof. Therefore, thecircular light beam formed by the diffractive optical element 61 forms acircular illumination field centering on the optical axis AX on theentrance surface of the micro fly's eye lens 8 through the zoom lens 7.In result, a circular secondary light source centering on the opticalaxis AX is formed on the rear side focal surface of the micro fly's eyelens 8 as well. In this case, an outer diameter of the circularsecondary light source can be changed as appropriate by changingmagnifications of the afocal zoom lens 5 or focal lengths of the zoomlens 7.

FIG. 4 is a view schematically showing a construction of the micro fly'seye lens of FIG. 3. Referring to FIG. 4, the micro fly's eye lens 8 isconstructed from the first fly's eye member 8 a arranged on the lightsource side and the second fly's eye member 8 b arranged on the maskside (irradiated surface side). Many first minute refraction surfaces 80a are vertically and horizontally and integrally formed on a surface onthe light source side (left of center in FIG. 4) of the first fly's eyemember 8 a. Meanwhile, many second minute refraction surfaces 80 b arevertically and horizontally and integrally formed on a surface on themask side of the second fly's eye member 8 b so that the second minuterefraction surfaces 80 b optically correspond to many first minuterefraction surfaces 80 a.

Here, each minute refraction surface is formed spherically, and has arectangular outer shape similar to the illumination region to be formedon the mask M. Therefore, a wavefront of a parallel light beam enteringthe micro fly's eye lens 8 is segmentalized by many first minuterefraction surfaces 80 a. Then, the parallel light beam sequentiallyreceives refraction actions of the first minute refraction surfaces 80 aand the corresponding second minute refraction surfaces 80 b. Afterthat, the light beam focuses on a rear side focal surface 80 c of themicro fly's eye lens 8. In result, many light sources as many as thenumber of the first minute refraction surfaces 80 a (then the number ofthe second minute refraction surfaces 80 b) are formed.

In this embodiment, the first fly's eye member 8 a is formed, forexample, by silica glass or fluorite, and the second fly's eye member 8b is formed, for example, by quartz crystal. Otherwise, the first fly'seye member 8 a is formed, for example, by fluorite, and the second fly'seye member 8 b is formed, for example, by silica glass. That is, nb, therefraction index of the optical material forming the second fly's eyemember 8 b is set larger than na, the refraction index of the opticalmaterial forming the first fly's eye member 8 a by, for example, 0.05 ormore.

Further, in this embodiment, the absolute value of the parameter βdefined by Formula (8) is set lower than 0.2. Here, the refraction indexdifference Δn in Formula (8) is given by a difference between nb, therefraction index of the optical material forming the second fly's eyemember 8 b and nc, a refraction index of a medium forming an atmosphereof the micro fly's eye lens 8 (nb−nc). That is, when the micro fly's eyelens 8 is arranged in the air, the refraction index difference Δn isgiven by (nb−1).

In this embodiment, as described above, nb, the refraction index of theoptical material forming the second fly's eye member 8 b is setrelatively large. Therefore, the refraction index difference Δn becomeslarge, then the absolute value of the parameter β is reduced. In result,it is possible to reduce change of the distortion aberration caused byvariations of surface shapes of the minute refraction surfaces of themicro fly's eye lens MF, then to reduce effects on the illuminationintensity distribution in the mask M and the wafer W based on theforegoing actions of the invention.

In the foregoing embodiment, the invention is applied to the micro fly'seye lens 8, wherein each minute refraction surface is formedspherically. However, application is not limited thereto. Such amodification (first modification) can be adopted that the invention isapplied to a cylindrical micro fly's eye lens, wherein each minuterefraction surface is formed cylindrically. FIG. 5 is a perspective viewschematically showing a construction of the cylindrical micro fly's eyelens according to the first modification of the embodiment.

Referring to FIG. 5, a cylindrical micro fly's eye lens 81 according tothe first modification of the embodiment is constructed from a firstfly's eye member 81 a arranged on the light source side and a secondfly's eye member 81 b arranged on the mask side. Cylindrical lens groups82 a and 82 b arranged along the X direction are formed with a pitch ofp1 respectively on each light source side of the first fly's eye member81 a and the second fly's eye member 81 b.

Meanwhile, cylindrical lens groups 83 a and 83 b arranged along the Zdirection are formed with a pitch of p2 respectively on each mask sideof the first fly's eye member 81 a and the second fly's eye member 81 b.Focusing attention on refraction action in terms of the X direction ofthe cylindrical micro fly's eye lens 81 (that is, refraction action interms of the XY plane), a wavefront of a parallel light beam enteringalong the optical axis AX is segmentalized with the pitch of p1 alongthe X direction by the cylindrical lens group 82 a formed on the lightsource side of the first fly's eye member 81 a. Then, the light beamreceives condensing action on the refraction surface thereof. Afterthat, the light beam receives condensing action on a refraction surfaceof a corresponding cylindrical lens among the cylindrical lens group 82b formed on the light source side of the second fly's eye member 81 b.Then, the light beam focuses on the rear side focal surface of thecylindrical micro fly's eye lens 81.

Meanwhile, focusing attention on refraction action in terms of the Zdirection of the cylindrical micro fly's eye lens 81 (that is,refraction action in terms of the ZY plane), a wavefront of a parallellight beam entering along the optical axis AX is segmentalized with apitch of p2 along the Z direction by the cylindrical lens group 83 aformed on the mask side of the first fly's eye member 81 a. Then thelight beam receives condensing action on the refraction surface thereof.After that, the light beam receives condensing action on a refractionsurface of a corresponding cylindrical lens among the cylindrical lensgroup 83 b formed on the mask side of the second fly's eye member 81 b.Then, the light beam focuses on the rear side focal surface of thecylindrical micro fly's eye lens 81.

As described above, the cylindrical micro fly's eye lens 81 of the firstmodification is constructed from the first fly's eye member 81 a and thesecond fly's eye member 81 b, wherein each cylindrical lens group isarranged on the both sides. However, the cylindrical micro fly's eyelens 81 demonstrates an optical function similar to of the micro fly'seye lens 8 constructed from the first fly's eye member 8 a and thesecond fly's eye member 8 b, wherein many minute refraction surfaceshaving the size of p1 in the X direction and the size of p2 in the Zdirection are vertically and horizontally and integrally formed.

When the invention is applied to the cylindrical micro fly's eye lens 81of the first modification, focusing on the refraction action in terms ofthe X direction, the refraction surfaces of the cylindrical lens group82 a formed on the light source side of the first fly's eye member 81 aconstruct the first minute refraction surfaces, and the refractionsurfaces of the cylindrical lens group 82 b formed on the light sourceside of the second fly's eye member 81 b construct the second minuterefraction surfaces. Further, focusing on the refraction action in termsof the Z direction, the refraction surfaces of the cylindrical lensgroup 83 a formed on the mask side of the first fly's eye member 81 aconstruct the first minute refraction surfaces, and the refractionsurfaces of the cylindrical lens group 83 b formed on the mask side ofthe second fly's eye member 81 b construct the second minute refractionsurfaces.

In the first modification, nb, the refraction index of the opticalmaterial forming the second fly's eye member 81 b is set larger than na,the refraction index of the optical material forming the first fly's eyemember 81 a, and the absolute value of the parameter β is set lower than0.2. Thereby, similarly to in the foregoing embodiment, in the firstmodification, change of the distortion aberration caused by variationsof surface shapes of the minute refraction surfaces of the cylindricalmicro fly's eye lens 81 can be reduced, and effects on the illuminationintensity distribution can be reduced.

Further, in the foregoing embodiment, the invention is applied to themicro fly's eye lens 8 constructed from the pair of fly's eye members 8a and 8 b. However, application is not limited thereto. It is possibleto adopt a modification (second modification), wherein the invention isapplied to an ordinary micro fly's eye lens constructed from a singleoptical member. FIG. 6 is a view schematically showing a construction ofthe micro fly's eye lens according to the second modification of thisembodiment.

In an ordinary micro fly's eye lens 84 constructed from a single opticalmember as shown in FIG. 6, many first minute refraction surfaces 84 aare formed vertically and horizontally and integrally on the lightsource side thereof, and many second minute refraction surfaces 84 b areformed vertically and horizontally and integrally on the mask sidethereof so that many second minute refraction surfaces 84 b opticallycorrespond to many first minute refraction surfaces 84 a. When theinvention is applied to the micro fly's eye lens 84 of the secondmodification, the micro fly's eye lens 84 is bisected by a virtualsegmentation surface 84 c perpendicular to the optical axis AX. Then, itis regarded that a portion on the light source side from thesegmentation surface 84 c constructs the first optical member, and aportion on the mask side from the segmentation surface 84 c constructsthe second optical member.

In the second modification, the micro fly's eye lens 84 is constructedfrom the single optical member. Therefore, differently from theforegoing embodiment, it is not possible to set a refraction index of anoptical material forming the second optical member larger than arefraction index of an optical material forming the first opticalmember. However, similarly to in the foregoing embodiment, in the secondmodification, change of the distortion aberration caused by variationsof surface shapes of the minute refraction surfaces of the micro fly'seye lens 84 can be reduced, and effects on the illumination intensitydistribution can be reduced by setting the absolute value of theparameter β lower than 0.2.

In the case of a scanning exposure type exposure apparatus, illuminationintensity nonuniformity in the scanning direction on the wafer W can bereduced by averaging effects by scanning exposure. Therefore, in themicro fly's eye lens (8, 81, and 84) used for the scanning exposure typeexposure apparatus, it is not necessary to satisfy the conditionalformula of the parameter β in terms of the direction (X direction)optically corresponding to the scanning direction (X direction) on thewafer W. However, it is necessary to satisfy the conditional formula ofthe parameter β in terms of the direction (Z direction) opticallycorresponding to the nonscanning direction (Y direction) on the wafer W.

However, it is general that in the micro fly's eye lens (8 and 84),wherein each minute refraction surface is formed spherically, therefracting power ratio γ and the refraction index difference Δn do notdepend on the directions but are constant, and the numerical aperture NAon the emission side in the nonscanning direction (Z direction) is setlarger than in the scanning direction (X direction). Therefore, whensetting is made so that the conditional formula of the parameter β issatisfied in terms of the nonscanning direction (Z direction) accordingto the invention, the conditional formula of the parameter β in terms ofthe scanning direction (X direction) is consequentially satisfied aswell.

Meanwhile, in the cylindrical micro fly's eye lens 81, wherein eachminute refraction surface is formed cylindrically, it is general thatthe refraction index difference Δn does not depend on the directions butis constant, and the numerical aperture NA on the emission side in thenonscanning direction is set larger than in the scanning direction.However, the refracting power ratio γ does not depend directions, andcan be set freely to some extent. Therefore, in this case, such anaspect can be adopted that the conditional formula of the parameter β issatisfied in terms of the nonscanning direction (Z direction), but theconditional formula of the parameter β in terms of the scanningdirection (X direction) is not always satisfied.

In the exposure apparatus in the foregoing embodiment (including themodifications), a micro device (semiconductor device, image pickupdevice, liquid crystal display device, thin film magnetic head and thelike) can be manufactured by illuminating the mask (reticle) by theillumination optical device (illumination step), and exposing thepattern for transfer formed on the mask on the photosensitive substrateby using the projection optical system (exposure step). Descriptionswill be hereinafter given of an example of a technique in obtaining asemiconductor device as a micro device by forming a given circuitpattern on a wafer or the like as a photosensitive substrate by usingthe exposure apparatus of the foregoing embodiment with reference to theflowchart of FIG. 7.

First, in Step 301 of FIG. 7, a metal film is deposited on one lot ofwafer. In the next Step 302, the metal film on the one lot of wafer iscoated with photoresist. After that, in Step 303, an image of a patternon the mask is sequentially exposed and transferred in each shot regionon the one lot of wafer through the projection optical system by usingthe exposure apparatus of the foregoing embodiment. After that, in Step304, the photoresist on the one lot of wafer is developed. Then, in Step305, etching is performed by using the resist pattern as a mask on theone lot of wafer. Thereby, a circuit pattern corresponding to thepattern on the mask is formed in each shot region on each wafer. Afterthat, for example, a circuit pattern of an upper layer is furtherformed, and thereby the device such as the semiconductor device ismanufactured. According to the foregoing method of manufacturingsemiconductor devices, it is possible to obtain a semiconductor devicehaving a very fine circuit pattern with good throughput.

Further, in the exposure apparatus of the foregoing embodiment, a liquidcrystal display device as a micro device can be also obtained by forminga given pattern (circuit pattern, electrode pattern and the like) on aplate (glass substrate). Descriptions will be hereinafter given of anexample of a technique used then with reference to the flowchart of FIG.8. In FIG. 8, in pattern formation step 401, so-called photolithographystep, wherein a pattern of a mask is transferred and exposed on aphotosensitive substrate (glass substrate or the like coated withresist) by using the exposure apparatus of the foregoing embodiment isperformed. By this photolithography step, a given pattern including manyelectrodes and the like is formed on the photosensitive substrate. Afterthat, the exposed substrate is provided with respective steps such asdevelopment step, etching step, and resist exfoliation step. Thereby, agiven pattern is formed on the substrate. The procedure is forwarded tothe next color filter formation step 402.

Next, in the color filter formation step 402, a color filter whereinmany groups constructed from three dots corresponding to R (Red), G(Green), and B (Blue) are arranged in a state of a matrix, or a colorfilter wherein a plurality of filter groups constructed from threestripes of R, G, and B are arranged in the direction of horizontalscanning line is formed. Then, after the color filter formation step402, cell assembly step 403 is performed. In the cell assembly step 403,a liquid crystal panel (liquid crystal cell) is assembled by using thesubstrate having the given pattern obtained in the pattern formationstep 401, the color filter obtained in the color filter formation step402 and the like. In the cell assembly step 403, the liquid crystalpanel (liquid crystal cell) is manufactured by, for example, injectingliquid crystal between the substrate having the given pattern obtainedin the pattern formation step 401 and the color filter obtained in thecolor filter formation step 402.

After that, in module assembly step 404, respective parts such as anelectric circuit for making display operation of the assembled liquidcrystal panel (liquid crystal cell) and a backlight are installed tocomplete the liquid crystal display device. According to the foregoingmethod of manufacturing liquid crystal display devices, it is possibleto obtain a liquid crystal display device having a very fine circuitpattern with good throughput.

In the foregoing embodiment, the mask M is illuminated in a state ofsuperimposition by condensing light from the secondary light source bythe condenser optical system 9. However, the invention is not limitedthereto. It is possible that an illumination field stop (mask blind) anda relay optical system for forming an image of this illumination fieldstop on the mask M are arranged in the optical path between thecondenser optical system 9 and the mask M. In this case, the condenseroptical system 9 condenses light from the secondary light source forilluminating the illumination field stop in a state of superimposition.The relay optical system forms the image of an aperture part (lighttransmittance part) of the illumination field stop on the mask M.

Further, in the foregoing embodiment, the KrF excimer laser light(wavelength: 248 nm) or the ArF excimer laser light (wavelength: 193 nm)is used as exposure light. However, the invention is not limitedthereto. The invention can be also applied to, for example, exposurelight having a wavelength of 300 nm or less. Further, in the foregoingembodiment, the invention has been described taking the example of theprojection exposure apparatus comprising the illumination opticaldevice. However, it is clear that the invention can be applied to ageneral illumination optical device for illuminating irradiated surfacesother than the mask.

INDUSTRIAL APPLICABILITY

As described above, in the invention, an optical integrator is set tosatisfy a conditional formula in terms of a parameter β. Therefore,change of a distortion aberration caused by variations of surface shapesof minute refraction surfaces of the optical integrator can be reduced,and then effects on an illumination intensity distribution on anirradiated surface can be reduced.

Therefore, in an illumination optical device of the invention, it ispossible to illuminate the irradiated surface under desired illuminationconditions by using the optical integrator, wherein effects ofmanufacturing errors of the minute refraction surfaces on theillumination intensity distribution are reduced. Further, in an exposureapparatus and an exposure method of the invention, a good device can bemanufactured by performing good projection exposure under goodillumination conditions by using the highly efficient illuminationoptical device capable of illuminating the irradiated surface under thedesired illumination conditions.

1. An optical integrator, comprising: an integrally formed plurality offirst minute refraction surfaces; and an integrally formed plurality ofsecond minute refraction surfaces, which are provided closer to a lightemission side than the plurality of first minute refraction surfaces sothat the plurality of second minute refraction surfaces opticallycorrespond to the plurality of first minute refraction surfaces, whereina parameter β satisfies the following conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where a refracting power ratioφa/φb between φa, a refracting power of the first minute refractionsurfaces and φb, a refracting power of the second minute refractionsurfaces is γ, numerical aperture on the emission side of the opticalintegrator is NA, and a difference between a refraction index of amedium on a light entrance side of the second minute refraction surfacesand a refraction index of a medium on a light emission side of thesecond minute refraction surfaces is Δn.
 2. The optical integratoraccording to claim 1, wherein the plurality of first minute refractionsurfaces and the plurality of second minute refraction surfaces areformed on the same optical member.
 3. The optical integrator accordingto claim 2, wherein the plurality of second minute refraction surfacescomprise aspherical surfaces.
 4. The optical integrator according toclaim 1, comprising: a first optical member having the plurality offirst minute refraction surfaces; and a second optical member having theplurality of second minute refraction surfaces arranged on a lightemission side of the first optical member.
 5. The optical integratoraccording to claim 4, wherein the plurality of second minute refractionsurfaces comprise aspherical surfaces.
 6. The optical integratoraccording to claim 1, wherein each minute refraction surface is formedspherically or aspherically.
 7. The optical integrator according toclaim 6, wherein the aspherical surface is a rotational symmetryaspherical surface or a rotational asymmetry aspherical surface.
 8. Theoptical integrator according to claim 1, which is used for an exposureapparatus, wherein a mask and a photosensitive substrate are relativelymoved in relation to the projection optical system along a scanningdirection, and thereby a pattern of the mask is projected and exposed onthe photosensitive substrate, wherein an absolute value of the parameterβ in terms of a direction optically approximately perpendicular to thescanning direction is set lower than an absolute value of the parameterβ in terms of the scanning direction.
 9. An illumination optical devicefor illuminating an irradiated surface, comprising: the opticalintegrator according to claim
 1. 10. The illumination optical deviceaccording to claim 9, wherein the optical integrator forms a lightintensity distribution in a given shape in an illumination region. 11.An exposure apparatus, comprising: the illumination optical deviceaccording to claim 9; and a projection optical system for projecting andexposing a pattern of a mask arranged on the irradiated surface on aphotosensitive substrate.
 12. The exposure apparatus according to claim11, wherein the pattern of the mask is projected and exposed on thephotosensitive substrate by relatively moving the mask and thephotosensitive substrate in relation to the projection optical systemalong a scanning direction, and wherein an absolute value of theparameter β in terms of a direction optically approximatelyperpendicular to the scanning direction is set lower than an absolutevalue of the parameter β in terms of the scanning direction.
 13. Anexposure method, comprising the steps of: illuminating a mask throughthe illumination optical device according to claim 9, and projecting andexposing an image of a pattern formed on the illuminated mask on aphotosensitive substrate.
 14. The exposure method according to claim 13,wherein the step of projecting and exposing an image of a pattern formedon the illuminated mask on a photosensitive substrate comprises the stepof projecting and exposing the pattern of the mask on the photosensitivesubstrate while relatively moving the mask and the photosensitivesubstrate in relation to the projection optical system along a scanningdirection, and wherein an absolute value of the parameter β in terms ofa direction optically approximately perpendicular to the scanningdirection is set lower than an absolute value of the parameter β interms of the scanning direction.
 15. A device manufacturing methodcomprising: exposing a photosensitive substrate with the exposure methodaccording to claim 13; and developing the photosensitive substrate. 16.An optical integrator, comprising, in the following order from a lightentrance side: a first optical member having an integrally formedplurality of first minute refraction surfaces; and a second opticalmember having an integrally formed plurality of second minute refractionsurfaces, which are provided to optically correspond to the plurality offirst minute refraction surfaces, wherein the first optical member andthe second optical member are separated by a space, that is filled witha gas, wherein a refraction index of an optical material forming thesecond optical member is set larger than a refraction index of anoptical material forming the first optical member, wherein the opticalintegrator is used for light having a wavelength of 300 nm or less,wherein the optical material forming the first optical member includesfluorite, and wherein the optical material forming the second opticalmember includes silica glass.
 17. The optical integrator according toclaim 16, satisfying the following condition:0.05≦nb−na, where the refraction index of the optical material formingthe first optical member is na, and the refraction index of the opticalmaterial forming the second optical member is nb.
 18. The opticalintegrator according to claim 16, wherein each minute refraction surfaceis formed spherically or aspherically.
 19. The optical integratoraccording to claim 18, wherein the aspherical surface is a rotationalsymmetry aspherical surface or a rotational asymmetry asphericalsurface.
 20. The optical integrator according to claim 16, which is usedfor an exposure apparatus, wherein a mask and a photosensitive substrateare relatively moved in relation to the projection optical system alonga scanning direction, and thereby a pattern of the mask is projected andexposed on the photosensitive substrate, wherein a parameter β satisfiesthe following conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where a refracting power ratioφa/φb between φa, a refracting power of the first minute refractionsurfaces and φb, a refracting power of the second minute refractionsurfaces is γ, a numerical aperture on the emission side of the opticalintegrator is NA, and a difference between a refraction index of amedium on a light entrance side of the second minute refraction surfacesand a refraction index of a medium on a light emission side of thesecond minute refraction surfaces is Δn, and wherein an absolute valueof the parameter β in terms of a direction optically approximatelyperpendicular to the scanning direction is set lower than an absolutevalue of the parameter β in terms of the scanning direction.
 21. Anillumination optical device for illuminating irradiated surface,comprising: the optical integrator according to claim
 16. 22. Theillumination optical device according to claim 21, wherein the opticalintegrator forms a light intensity distribution in a given shape in anillumination region.
 23. An exposure apparatus, comprising: theillumination optical device according to claim 21; and a projectionoptical system for projecting and exposing a pattern of a mask arrangedon the irradiated surface on a photosensitive substrate.
 24. Theexposure apparatus according to claim 23, wherein the pattern of themask is projected and exposed on the photosensitive substrate byrelatively moving the mask and the photosensitive substrate in relationto the projection optical system along a scanning direction, wherein aparameter β satisfies the following conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where a refracting power ratioφa/φb between φa, a refracting power of the first minute refractionsurfaces and φb, a refracting power of the second minute refractionsurfaces is γ, a numerical aperture on the emission side of the opticalintegrator is NA, and a difference between a refraction index of amedium on a light entrance side of the second minute refraction surfacesand a refraction index of a medium on a light emission side of thesecond minute refraction surfaces is Δn, and wherein an absolute valueof the parameter β in terms of a direction optically approximatelyperpendicular to the scanning direction is set lower than an absolutevalue of the parameter β in terms of the scanning direction.
 25. Anexposure method, comprising the steps of: illuminating a mask throughthe illumination optical device according to claim 21, and projectingand exposing an image of a pattern formed on the illuminated mask on aphotosensitive substrate.
 26. The exposure method according to claim 25,wherein the step of projecting and exposing an image of a pattern formedon the illuminated mask on a photosensitive substrate comprises the stepof projecting and exposing the pattern of the mask on the photosensitivesubstrate while relatively moving the mask and the photosensitivesubstrate in relation to the projection optical system along a scanningdirection, wherein a parameter β satisfies the following conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where a refracting power ratioφa/φb between φa, a refracting power of the first minute refractionsurfaces and φb, a refracting power of the second minute refractionsurfaces is γ, a numerical aperture on the emission side of the opticalintegrator is NA, and a difference between a refraction index of amedium on a light entrance side of the second minute refraction surfacesand a refraction index of a medium on a light emission side of thesecond minute refraction surfaces is Δn, and wherein an absolute valueof the parameter β in terms of a direction optically approximatelyperpendicular to the scanning direction is set lower than an absolutevalue of the parameter β in terms of the scanning direction.
 27. Anexposure apparatus, comprising: an illumination optical system includingan optical integrator; and a projection optical system for forming apattern image of a mask on a photosensitive substrate, wherein thepattern of the mask is projected and exposed on the photosensitivesubstrate while the mask and the photosensitive substrate are relativelymoved in relation to the projection optical system along a scanningdirection, wherein the optical integrator comprises: an integrallyformed plurality of first minute refraction surfaces; and an integrallyformed plurality of second minute refraction surfaces, which areprovided closer to a light emission side than the plurality of firstminute refraction surfaces so that the plurality of second minuterefraction surfaces optically correspond to the plurality of firstminute refraction surfaces, and wherein a parameter β satisfies thefollowing conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where a refracting power ratioφa/φb between φa, a refracting power of the first minute refractionsurfaces in terms of a non-scanning direction optically approximatelyperpendicular to the scanning direction and φb, a refracting power ofthe second minute refraction surfaces in terms of the non-scanningdirection is γ, numerical aperture on the emission side in terms of thenon-scanning direction of the optical integrator is NA, and a differencebetween a refraction index of a medium on a light entrance side of thesecond minute refraction surfaces and a refraction index of a medium ona light emission side of the second minute refraction surfaces is Δn.28. An exposure method, comprising the steps of: illuminating a maskthrough the illumination optical device including an optical integrator,and projecting and exposing an image of a pattern formed on theilluminated mask on a photosensitive substrate, wherein the step ofprojecting and exposing an image of a pattern formed on the illuminatedmask on a photosensitive substrate comprises the step of projecting andexposing the pattern of the mask on the photosensitive substrate whilerelatively moving the mask and the photosensitive substrate in relationto the projection optical system along a scanning direction, wherein theoptical integrator comprises: an integrally formed plurality of firstminute refraction surfaces; and an integrally formed plurality of secondminute refraction surfaces, which are provided closer to a lightemission side than the plurality of first minute refraction surfaces sothat the plurality of second minute refraction surfaces opticallycorrespond to the plurality of first minute refraction surfaces, andwherein a parameter β satisfies the following conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where a refracting power ratioφa/φb between φa, a refracting power of the first minute refractionsurfaces in terms of a non-scanning direction optically approximatelyperpendicular to the scanning direction and φb, a refracting power ofthe second minute refraction surfaces in terms of the non-scanningdirection is γ, numerical aperture on the emission side in terms of thenon-scanning direction of the optical integrator is NA, and a differencebetween a refraction index of a medium on a light entrance side of thesecond minute refraction surfaces and a refraction index of a medium ona light emission side of the second minute refraction surfaces is Δn.29. A device manufacturing method comprising: exposing a photosensitivesubstrate with the exposure method according to claim 28; and developingthe photosensitive substrate.
 30. An exposure method comprising:introducing a radiation from a source to a plurality of first minuterefraction surfaces which are integrally formed on a first member of anoptical integrator; introducing a radiation from the first minuterefraction surfaces to a plurality of second minute refraction surfaceswhich are integrally formed on a second member of the opticalintegrator, and which optically correspond to the plurality of the firstminute refraction surfaces; illuminating a pattern with a radiation fromthe optical integrator; and projecting a pattern image on aphotosensitive substrate while moving the photosensitive substrate alonga scanning direction, wherein a parameter β satisfies the followingconditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where a refracting power ratioφa/φb between φa, a refracting power of the first minute refractionsurfaces in terms of a non-scanning direction optically approximatelyperpendicular to the scanning direction and φb, a refracting power ofthe second minute refraction surfaces in terms of the non-scanningdirection is γ, a numerical aperture on the emission side in terms ofthe non-scanning direction of the optical integrator is NA, and adifference between a refraction index of a medium on a light entranceside of the second minute refraction surfaces and a refraction index ofa medium on a light emission side of the second minute refractionsurfaces is Δn.
 31. A device manufacturing method comprising: exposing aphotosensitive substrate with the exposure method according to claim 30;and developing the photosensitive substrate.
 32. An exposure methodcomprising: introducing a radiation from a source to a plurality offirst minute refraction surfaces which are integrally formed on a firstoptical member of an optical integrator; introducing a radiation fromthe first minute refraction surfaces to a plurality of second minuterefraction surfaces which are integrally formed on a second opticalmember of the optical integrator, and which optically correspond to theplurality of first minute refraction surfaces; illuminating a patternwith a radiation from the optical integrator; and projecting a patternimage on a photosensitive substrate while moving the photosensitivesubstrate along a scanning direction, wherein the first optical memberand the second optical member are separated by a space, that is filledwith a gas, wherein a refraction index of an optical material formingthe second optical member is set larger than a refraction index of anoptical material forming the first optical member, wherein the radiationfrom the source includes light having a wavelength of 300 nm or less,wherein the optical material forming the first optical member includesfluorite, and wherein the optical material forming the second opticalmember includes silica glass.
 33. A device manufacturing methodcomprising: exposing a photosensitive substrate with the exposure methodaccording to claim 32; and developing the photosensitive substrate. 34.A method of manufacturing an optical integrator comprising: integrallyforming a plurality of first minute refraction surfaces on the opticalintegrator; and integrally forming a plurality of second minuterefraction surfaces on the optical integrator, the second minuterefraction surfaces optically corresponding to the plurality of firstminute refraction surfaces, wherein a parameter β satisfies thefollowing conditions:|β|<0.2 (where β=(γ−1)³ ·NA ² /Δn ²), where a refracting power ratioφa/φb between φa, a refracting power of the first minute refractionsurfaces in terms of a non-scanning direction optically approximatelyperpendicular to the scanning direction and φb, a refracting power ofthe second minute refraction surfaces in terms of the non-scanningdirection is γ, a numerical aperture on the emission side in terms ofthe non-scanning direction of the optical integrator is NA, and adifference between a refraction index of a medium on a light entranceside of the second minute refraction surfaces and a refraction index ofa medium on a light emission side of the second minute refractionsurfaces is Δn.
 35. The method according to claim 34, wherein theplurality of first minute refraction surfaces are formed on a firstmember of the optical integrator, and wherein the plurality of firstminute refraction surfaces are formed on a second member of the opticalintegrator.
 36. The method according to claim 35, further comprising:arranging the first member and the second member separately from eachother.
 37. An optical integrator manufactured by the method according toclaim
 34. 38. A method of manufacturing an optical integratorcomprising: integrally forming a plurality of first minute refractionsurfaces on a first optical member of the optical integrator; integrallyforming a plurality of second minute refraction surfaces on a secondoptical member of the optical integrator, the second minute refractionsurfaces optically corresponding to the plurality of first minuterefraction surfaces; and arranging the first optical member and thesecond optical member separately from each other, with a gas-filledspace between the first and second optical members, wherein a refractionindex of an optical material forming the second optical member is setlarger than a refraction index of an optical material forming the firstoptical member, wherein the optical integrator is used for lightincluding a wavelength of 300 nm or less, wherein the optical materialforming the first optical member includes fluorite, and wherein theoptical material forming the second optical member includes silicaglass.